Mani is a minor supporting character in the film Yu-Gi-Oh!: The Dark Side of Dimensions, closely tied to the antagonists Aigami and Sera. His background begins in a harsh childhood: he, along with Aigami, Sera, and other orphans, lived under the care of an abusive man. The man was killed by Shadi, the guardian of the Millennium Items, after which Shadi took the orphans into his protection. Mani and the others came to regard Shadi as a father figure, living with him until Shadi was murdered.

After Shadi's death, Mani aligned himself with Aigami and Sera, sharing their grief and their desire for revenge. He appears early in the film at the excavated ruins of the Shrine of the Underworld, wearing a hooded cloak. Later, he is seen observing Yugi and his friends from a distance alongside Aigami and Sera.

Mani's role in the story is primarily as a follower of Aigami's plan. He becomes a victim of the Millennium Ring's corrupting influence. During a confrontation in the alternate dimension created by Aigami's Quantum Cube, Mani is warped by the dark energy of the Millennium Ring. Under this influence, he attacks Ryo Bakura, intending to kill him. Aigami tries to stop him, and Mani briefly resists his own actions before being engulfed by the Ring's power and disappearing into another dimension.

Mani's key relationships are with Aigami and Sera, his fellow orphans and allies. His loyalty to them is rooted in their shared traumatic past and their reverence for Shadi. His development is limited; he does not undergo a major arc but instead serves as a tragic example of how the Millennium Items' malevolent energy can consume someone. His notable ability, beyond being a Duel Monsters player, is that the Millennium Ring grants him a temporary but dangerous increase in power, though it ultimately strips him of his free will. His disappearance leaves his fate ambiguous, but he does not return by the film's end.